Eurasian water-milfoil (Myriophyllum spicatum)

An emergent, herbaceous aquatic plant, Eurasian watermilfoil, usually extends 3 to 10 feet, but can reach as much as 33 feet in length. The stems are reddish-brown to whitish-pink. It forms dense mats on the surface of water bodies, and new plants that may emerge from each node on a stem root on contact with mud. Regenerates mostly from rhizomes, fragmented stems, and axillary buds that develop throughout the year. Eurasian watermilfoil can be found in nearly 400 WI lakes.

Overview

Eurasian water-milfoil is Restricted (Orange counties)

Other names for this plant include:

Common names: European watermilfoil, spike water-milfoil

Scientific names: Myriophyllum spicatum var. muricatum

Ecological threat:

Invades lakes, rivers, and other water bodies ranging from fresh to brackish; thrives in areas that have been subjected to various kinds of natural and manmade disturbance.

Can form large, floating mats of vegetation on the surface of water bodies, preventing light penetration for native aquatic plants and impeding water traffic.

Winter-hardy, able to overwinter in frozen lakes and ponds in northern states and Canada; also able to grow in shallow, over-heated bays such as Chassahowitzka Bay in FL.

Species Assessment Groups (SAG) were assembled to recommend a legal classification for each species considered for NR 40. The recommendation for Eurasian water-milfoil was based upon this literature review developed by the department.

Identification

Leaves: Greyish-green and finely divided pairs of fine, thin leaflets about ½-2” long; leaflets give milfoil a feathery appearance that is a distinguishing feature of the plant. Arranged in whorls of 3-6 leaves about the stem.

Flowers: Small, yellow or reddish, 4-parted flowers on a spike that projects 2-4 inches above the water surface.

Fruits & seeds: A hard, segmented capsule containing four seeds.

Roots: Fibrous, often developing on plant fragments.

Similar species: Myriophyllum spicatum might be confused with a number of other submersed plants, including other water-milfoils and other submersed plants. Native northern water-milfoil (Myriophyllum sibiricum = M. exalbescens) has fewer than 12 leaf segments on each side of the leaf axis, whereas Eurasian water-milfoil leaves have 14 or more leaf segments on each side of the leaf axis; and has somewhat stouter stems than does Eurasian water-milfoil. Native coontail (Ceratophyllum demersum) has leaves that are toothed and the plant feels rough when pulled through the hand, whereas Eurasian water-milfoil leaves are not toothed and the plant does not feel rough.

Distribution

Do you know of additional Eurasian water-milfoil populations? Send us a report.

Control

Chemical: Herbicides used to control milfoil include 2,4-D, triclopyr, fluridone, endothall or diquat. Although middle to late summer is when plants tend to reach the surface and create a nuisance, most chemical applications for milfoil are done in the spring during early stages of active growth. This reduces the effects on native plants. An aquatic applicator license is needed to apply chemicals in most aquatic treatments.

Manual: Hand-pulling by snorkelers or divers can be an effective removal strategy for small populations of plants. It can be used as a follow-up to chemical control to remove surviving plants. Care must be taken to remove all pieces of the plant, because even small fragments can survive and re-root.

Biological: The native milfoil weevil can be stocked in lakes. The weevils feed on the plants, and the larvae burrow into the stems. They do not eat other types of plants, and reduce the vigor of the milfoil population.